BAGHDAD — Men dressed as Iraqi soldiers abducted 18 Sunnis, whose bullet-ridden corpses turned up in farmland just south of Baghdad, authorities said Friday, a grim reminder of the worst days of sectarian killings that plagued the country after the U.S. invasion. Police said officers later discovered the beheaded corpses of three men in Baghdad's eastern suburbs, their hands tied behind their backs, part of attacks that killed 22 others Friday. The apparently targeted killings come after similar killings earlier this week, raising fears that the country, already embroiled in months of rising violence, could see the return of Shiite and Sunni Muslim death squads roaming the streets. "These recent killings show that the fears by many Iraqis that their country is heading to darker days similar to 2006-2007 are true and that the wounds of the past are not healed yet," Baghdad-...